1. Field of the Invention
The present invention relates to a process for manufacturing cut threads from threads coated with a mixture in the liquid state which can react under the effect of actinic radiation. More specifically, the invention relates to a process for manufacturing cut threads from continuous threads intended in particular for use as reinforcements such as glass threads, said threads being composed of filaments coated with a sizing composition based on compounds which can react under the effect of actinic radiation. The present invention also relates to a device for performing this process.
2. Description of the Related Art
Cut threads are commonly used for reinforcing various matrices such as thermoplastic resins thermosetting resins, plaster, cement or paper.
It is known to manufacture these cut threads directly from one or more fiber-drawing installations in the following manner: Thin streams of molten glass flowing from the apertures in one or a plurality of die plates are drawn mechanically into filaments and are then coated in the latter form with a sizing composition before being collected into threads. The threads are then cut. The threads are mechanically drawn by the anvil wheel of the cutting member.
The size used for coating the filaments inter alia enables the filaments to be bonded to one another and the threads to be protected against abrasion, while imparting thereto the properties which are essential for the subsequent transformations. The sizes most commonly used are aqueous sizes which normally comprise of the order of 90% (weight) water. This considerable amount of water can have a harmful effect on the correct development of the process and renders necessary the provision of means for reducing the moisture content at different stages.
Before cutting, some of the water is eliminated by rubbing on the filament-assembly device. This reduction of the moisture content can, nevertheless, prove to be inadequate. Adhesion of the threads to one another can in particular occur after cutting as can adhesion of these same threads to the devices used for their collection. Means for reducing the moisture before cutting exist, in particular those described in patent WO 92/05122.
Further means exist for reducing the moisture content after cutting and before use of the cut threads for reinforcing matrices, it being possible for the water to impair the good adhesion between the glass and matrix and the ageing properties of the resultant composite. Patent FR 2 253 716 thus describes a process for manufacturing cut threads, during which process the moisture content of the threads is reduced after cutting by passing the cut threads under a series of infrared lamps or through an air-circulating oven.
However, the drying stage or stages can restrict productivity or necessitate the use of relatively heavy devices while requiring greater energy consumption.
Other processes are known for continuous threads, in particular a process in which a mixture which reacts under the effect of UV radiation is deposited on filaments during the fiber-drawing operation before these filaments are gathered together to form at least one thread, and the thread or threads is or are exposed to UV radiation during the fiber-drawing process. This process, described in patent EP-B1-243 275 makes no mention of a drying stage but requires operating with highly reactive sizing compositions in the presence of a large content of photoinitiators owing to the high fiber-drawing speed of the filaments below the die plate. In addition, the threads obtained according to this process do not easily withstand bending and tearing when being cut and problems relating to flocking or disintegration can occur in the devices performing this operation.